Aliphatic-aromatic copolymers

Owing to their pronounced hydrolytic instability, polyanhydrides have therefore been explored as degradable implant materials. Aliphatic polyanhydrides degrade within days whereas some aromatic polyanhydrides degrade over several years. Thus, aliphatic-aromatic copolymers, having intermediate rates of degradation, are usually employed. 

Fluorinated rubbers, copolymers of hexafluoropropylene and vinylidene-fluorides, have excellent resistance to oils, fuels and lubricants at temperatures up to 200°C. They have better resistance to aliphatic, aromatic and chlorinated hydrocarbons and most mineral acids than other rubbers, but their high cost restricts their engineering applications. Cheremisinoff et al. [54] provide extensive physical and mechanical properties data on engineering plastics. A glossary of terms concerned with fabrication and properties of plastics is given in the last section of this chapter. 

M.D. Shelby, A.J. Matosky, C.M. Tanner, and M.E. Donelson, Blends of aliphatic-aromatic copolyesters with ethylene-vinyl acetate copolymers, US Patent 7 241838, assigned to Eastman Chemical Company (Kingsport, TN), July 10,2007. 

MVE/MAN Copolymem. Various iuol wl grades of polv(melliyl vinyl ether-co-maleic anhydride) (PMVEMA) are available. PMVEMA, supplied as a white, fluffy powder, is soluble in ketones, esters, pyridine, lactams, and aldehydes, and insoluble in aliphatic, aromatic, or halogenated hydrocarbons, as well as in ethyl ether and nitroparaffins. When the copolymer dissolves in water or alcohols, the anhydride group is cleaved, forming the polymers in free acid form or the half-esters of the corresponding alcohol, respectively. 

Polyanhydrides Polyanhydrides have a hydrophobic backbone with a hydrolytically labile anhydride linkage. These polymers widely vary in chemical composition and include aliphatic, aromatic, and fatty acid-based polyanhydrides. The rate of degradation depends on the chemical composition of the polymer. In general, aliphatic polyanhydrides degrade more rapidly than the aromatic polymer. Hence, copolymer blends with varying ratios of aliphatic-to-aromatic polyanhydrides can be synthesized to suit specific applications. 

Manufacture. Propylene oxide is copolymerized with allyl glycidyl ether in an aliphatic, aromatic, or chlorinated hydrocarbon solution using Vandenberg-type catalysts. A complete conversion and a uniform copolymer is obtained containing about 6% of AGE. 

According to literary data, the following mixtures of aromatic/aliphatic-aromatic hydrocarbons were separated toluene/ n-hexane, toluene/n-heptane, toluene/n-octane, toluene/f-octane, benzene/w-hexane, benzene/w-heptane, benzene/toluene, and styrene/ethylbenzene [10,82,83,109-129]. As membrane media, various polymers were used polyetherurethane, poly-esterurethane, polyetherimide, sulfonyl-containing polyimide, ionicaUy cross-linked copolymers of methyl, ethyl, n-butyl acrylate with acrilic acid. For example, when a composite polyetherimide-based membrane was used to separate a toluene (50 wt%)/n-octane mixture, the flux Q of 10 kg pm/m h and the separation factor of 70 were achieved [121]. When a composite mebrane based on sulfonyl-containing polyimide was used to separate a toluene (1 wt%)/ -octane mixture, the flux 2 of 1.1 kg pm/m h and the separation factor of 155 were achieved [10]. When a composite membrane based on ionically cross-linked copolymers of methyl, ethyl, w-butyl acrylate with acrilic acid was used to separate toluene (50 wt%)//-octane mixture, the flux Q of 20-1000 kg pm/m h and the separation factor of 2.5-13 were achieved [126,127]. 

A number of commercially significant PC copolymers are produced. In addition to the previously discussed branched PCs (for extrusion and blow-molding applications) and copolymers of BPA with tetrabromo-BPA for enhanced flame retardancy, high-Tg polyester carbonate copolymers have been produced for a number of years (Bayer Apec , GE LEXAN PPC Tg approximately 190°C). Polyester carbonate copolymers can be produced via copolymerization of BPA with diacyl chlorides. Aromatic diadds produce high-Tg copolymers, while aliphatic diadds yield lower-Tg copolymers. A lower-Tg PC aliphatic polyester copolymer (GE LEXAN SP resin) exhibits enhanced flow and ductility in comparison to standard PC and is useful for thin-wall injection molding applications requiring ductility and ease of melt processability, such as personal communication devices. GE has recently introduced two new PC copolymers, a PC-siloxane copolymer (LEXAN EXL) and a copolymer of... 

By far the largest group of liquid crystalline polymers containing imide groups are copoly(esterimide)s (PEIs). These have been sub-divided into flexible copolymers containing aliphatic spacers and wholly aromatic copolymers. There are several reports of copoly(amide-imide)s and copoly(ether-imide)s (both thermotropic and lyotropic) and these are treated separately. There are only a few examples of wholly aromatic imide containing LCPs, as polyimides frequently melt well above their decomposition temperature. Successful attempts have been made to incorporate flexible spacers, but in most instances the spacers are based on ether units, and the polymer is more strictly classified as a poly(etherimide). 

The aliphatic-aromatic diacid monomers were prepared from the reaction of bromoalkanoic acid methyl ester and p-hydroxy benzoic acid methyl ester. The polymers of carboxyphenoxy alkanoic add of n = 3, 5, and 7 methylenes were soluble in chlorinated hydrocarbons and melted at temperatures below 100 °C. Copolymers of these monomers melted at lower temperatures than the respective homopolymers. These polymers displayed zero-order hydrolytic degradation profile ranging from 2 to 10 weeks. Increasing the length of the alkanoic chain, decreased the degradation rate of the polymer (Fig. 3). 

The melting point, as determined by differential scanning calorimeter, of these aromatic polyanhydrides is mnch higher than aliphatic polyanhydrides. The melting point of aliphatic-aromatic copolyanhydrides is proportional to aromatic content. For this type of copolymers, there is characteristically a minimnm between 5 and 20mol% of lower-melting component. The introdnction of fatty acids in the copolymer chain lowers the melting point as compared to that of bulk polymer [14]. 

Hydrocarbons such as dibenzyl toluene and products with an aliphatic-aromatic structure are used as extenders for immersion and rotation molding pastes. Polyamide flexibilizing with the help of plasticizers with comparable polar structures (e.g., Cetamoll in the sulfamide group), has receded into the background ever since the development of PA copolymers with elastomeric qualities that are for the most part resistant to low temperatures. 

For aliphatic-aromatic PBS copolymers, the enzymatic biodegradation rate decreases with increasing aromatic comonomer content (Honda et al. 2003 Li et al. 2007), as indicated in Fig. 19. 

Blends of aliphatic-aromatic polyester (75-25 parts) and poly(lactic acid) (25-75 parts) have been compatibilized through extrusion with a copolymer of styrene, GMA, and isomethacrylates (0-5 parts) (Hale 2008). Polyesters included those derived from adipic acid-terephthalic acid-butanediol. Mechanical properties were greatly improved compared to those for blends with no compatibiUzer. 

Blending of starch with aliphatic polyesters improves their processability and biodegradability Particularly suitable polyesters are poly(s caprolactone) and its copolymers, or polymers of higher melting point formed by the reaction of 1,4-butandiol with succinic acid or with sebacic acid, azelaic acid, or polydactic acid), poly(hydroxyalkanoates), and aliphatic-aromatic polyesters. 

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